Dairy industry sewage sludge as a fertilizer for an acid soil: a laboratory experiment with Lolium multiflorum L.

Abstract

The aim of this study was to assess the efficacy of dairy industry sewage sludge as a fertilizer for an acid soil, and to evaluate the leaching of its nutrients and pollutants. The sludge was applied to pots containing an acid pasture soil (pH 4.4, organic matter 9.6%) in which Lolium multiflorum was then sown. Two different doses of sewage sludge (80 and 160 cubic m ha-1) and a dose of 15:15:15 NPK (675 kg ha-1) were compared. Changes in soil properties (leachate and soil fraction) and the production and nutritional status of the crop were monitored for nine weeks. The addition of the sludge led to substantial increases in crop production, which was attributed to improvements in crop nutrient concentrations (mainly N and P) and soil properties (pH, total N and available P). The sludge-treated soils lost less NO3, Ca, Mg and K through leaching than those treated with the mineral fertilizer. The amounts of nutrient accumulated in the crop showed, however, that the input of K and to a lesser extent of Mg, were insufficient to cover requirements. Supplements of these elements are therefore necessary.